1. Field of the Invention
This invention relates to feed mechanisms and methods for feeding sheets and envelopes from a stack into a utilization device.
2. Background Information
Current estimates place the number of envelopes used annually in the United States at over 100 billion. A significant percentage of these envelopes are used in connection with bulk mailings, and are accordingly filled, addressed and processed by a variety of automated machines. A lynchpin of all automated processes is the automatic envelope inserter. Automatic inserters are large, complex machines that are loaded with contents to be inserted (e.g., individual letter sheets and/or fillers) and envelopes in which these contents are to be inserted. Other machines such as binders, that bind inserts together (into a books, catalogs, newspapers or magazines), presses that apply logos and decoration, addressing machines, collating and a variety of other machines are also used selectively to process individual sheet-like materials in bulk mailing and other processes. These various devices can be termed generally xe2x80x9cutilization devicesxe2x80x9d as they utilize sheet-like materials that are typically dispensed in stacks.
FIG. 1 shows a high-volume envelope inserter in current use by industry. The exemplary inserter 100 is a large, modular unit that combines various contents stored in hoppers (not shown) in the rear 102 of the machine and that directs (arrows 104 and 106) contents 105 onto a raceway 108 downstream (arrow 110) toward a stack of envelopes 112. At each point along the raceway, additional insert sheets are added to the contents. These contents may be folded, or otherwise compacted, to fit within the selected envelope by mechanism within the inserter. Envelopes are drawn from the stack 112, and directed downstream (arrow 114) to a inserting station 116 at which the closed-but-unsealed envelope flaps 118 are opened so that the final contents 120 can be inserted thereinto. The filled envelopes 122 are then transferred further downstream (arrow 124) to a stacking position or further-processing module (not shown).
Industrial inserters, referred to generically as swing-arm inserters, are available from a variety of well-known companies including Bell and Howell (Phillipsburg), as well as by Mailcrafter (Inserco model), Pitney Bowes (AMOS model), EMC Document System (Conquest Lsi model) and H M Surchin (Cornish model). A rotary variation is made by Buhrs (BB300 and BB 500) series. One more-specific example is the Bell and Howell Imperial(trademark).
Most inserters cycle at least 10,000 per hour without any material. However, once the various hopper materials are inserted into the envelopes, the net production is significantly slower. Due to paper handling problems, swing-arm inserters often net less than one third of their capabilities. A typical swing-arm machine in production may net less than 3000 completed envelopes per hour. After careful study, it is now recognized that the primary cause is the unreliable feeding of materials from the hoppers onto the collating raceway. The hopper is subject to jams, double feeds and no feeds. The design of these hoppers has not changed significantly in 30 years. And for that matter, they have changed little since their invention 60 years ago, as exemplified by U.S. Pat. No. 2,325,455.
With reference to FIG. 1, the envelope stack 112, the stacking location or xe2x80x9cfeed stationxe2x80x9d 130 consists of a series of upright guide rails 132, 134 that, respectively, contain the four opposing sides of each envelope in the stack.
As also shown in FIG. 1, the contents 105 entering the raceway originate from separate feed hoppers 150, 152, and 154. The hoppers include separate stacks of folded or unfolded sheet material 158. Each stack 158 represents a piece of the total inserted package 120 to be provided to the downstream envelope 118. The number of hoppers used varies based upon the number of content sheets to be inserted. For the purposes of illustration, further reference will be made to the hopper 154, which is the first hopper along the raceway 108. The hopper includes a rear backing guide 160 and a pair of front corner guides 162. The guides 160 and 162 essentially contain the stack of materials 158 so that bottom sheets can be stripped and directed (arrow 104) one at a time into the raceway 108.
With further reference to FIGS. 2-6, a content feed hopper and associated feeding and singulating assembly is shown in further detail, according to a prior art implementation. The stack of sheet-like materials (envelope inserts) 158 is confronted by a front stop 170 that retains the stack against forward movement into the raceway area. The stack is suspended at its rear (adjacent to the rear guide 160) by a partial floor 172. An opening 174 is defined between the front edge of the floor 172 and the front stop 170. This opening defines the region through which bottom sheets 176 are allowed to pass out of the stack and into the raceway, as will be described. At the bottom of the front stop 170 is located an adjustable pin 180 that is implemented as a threaded thumb screw with a projecting conical point 182. As shown in the plan view of FIG. 6, there are two pins 180 located at a horizontal spacing along the front stop 170. These pins are used to retain the front end of the stack of materials 158 from entering the opening 174. The pins are adjusted fairly finely because the points, if overly retracted, will not support the stack, while if overly projecting, will tear or prevent the bottom sheet 176 from passing over the pin 182 and into the opening when needed.
More particularly, FIGS. 3-5 show the general sequence by which a conventional vacuum sucker assembly 190 is used to draw bottom sheets 176 from the stack of materials 158. The sucker assembly 190 consists of a moving bracket arm 192 mounted on a common rotating shaft 194. In the illustrated example, the shaft moves an associated sucker assembly on each feed hopper simultaneously. The operative element of the sucker assembly 190 is a vacuum lead tube 196 that is adjustable upwardly and downwardly (double arrow 198 in FIG. 2) and rotationally (double curved arrow 200 in FIG. 2) using associated turn screws 202 and 204, respectively. These adjustments bring a suction cup 210 at the end of the feed tube 196 into a desired alignment with respect to the bottom of the stack. As will be described, these adjustments are problematic, and must be attended to regularly.
Referring to the feed operation in FIG. 3, the suction cup 210 engages the bottom sheet 176 and then draws it downwardly in a rotational motion as shown beneath the bottom edge of the front stop 170, having overcome the holding force of the pin point 182xe2x80x94in a generally downward-peeling motion away from the overlying stack. A moving hold-down finger 212 retracts to allow the rotational downward movement of the sheet 176, and then returns to the position shown in FIG. 3, in which it interferes with any return upward movement of the sheet 176. In accordance with FIG. 4, once the finger 212 is brought back into interfering contact with the sheet 176, the suction cup drops its vacuum and continues on its rotational path away from interference with the sheet 176. Just prior to the disengagement, a jawed gripper or xe2x80x9cpluckerxe2x80x9d assembly 220 moves into engagement with the forward edge of the sheet 176. The forward edge has been restrained by the finger 212 to enable an accurate grip upon the sheet 176. Once grip is achieved, the mechanism causes the upper jaw 222 to close against the lower jaw 224, and thereby firmly grasp the sheet. The gripper assembly 220 then rotates as shown in FIG. 5 (double arrow 226). When the gripper assembly 220 has swung sufficiently, the upper jaw and lower jaw, 222 and 224, pass between a set of stripper guides 230 that, in this example are a pair of upright, angled plates. The stripped guides engage the front edge of the sheet 176 at approximately the same time that the upper jaw 222 of the assembly 220 opens with respect to the lower jaw 224. The sheet, hence, is unable to move past stripper guides and is forced to fall away from the gripper assembly 220 and into the raceway 108. It becomes captured by opposing edge guides 232 and 234 and is moved along the raceway by a set of chain lugs 240 that push the upstream edge in a downstream direction (arrow 244 in FIG. 6).
As described generally above, the removal of sheets from the hopper stack involves accurate and complex sequential phasing of the individual mechanism elements. If any element is out of time or not accurately aligned, the fed sheets may become jammed or otherwise fail to feed properly. For example, the pins 182, while supporting the stack 158, and allowing singulation of the bottom sheet 176, often do so at the expense of producing a tear in the sheet as it is peeled past the pin""s sharp points. These two screw-adjusted pins are independently operator adjustable and since they are tapered, interact with the chosen sucker height adjustmentxe2x80x94the sucker itself being subject to several adjustments that further contemplate the delicate balance.
Specifically, the sucker requires two difficult, interrelated operator adjustments, one to tilt the sucker in-and-out and the other to raise it up-and-down. Due to the interrelationship, the in/out adjustment also raises and lowers the sucker, but in a non-linear, not-easily predictable way. For example, the operator may desire to screw in the pins to attain a more-aggressive singulation. Screwing the pins in raises the stack. They are then faced with two possible sucker adjustments to raise the sucker to follow the stack. They may inadvertently choose the incorrect tilt adjustment (which both raises and tilts the sucker, and unbalances the feeding) rather than the correct up/down adjustment.
In the prior art, to help with the reduction of feeding multiple sheets, the inserter manufactures provide an adjustable hopper floor plate, referred to as a T-plate. That is movable to increase or decrease the opening 174 size, depending upon how stiff or flexible the sheets are. Its purpose is to increase the stiffness of the sheet being peeled down by the sucker. This increases the deflecting force and helps prevent the sucker from dragging more than one sheet down at a time.
There are also several significant disadvantages to the above-described T-plate arrangement. It is difficult for an operator to know how to adjust the location of the plate forwardly or rearwardly, and it is highly dependent on the particular characteristics of a type (or even batch) of sheet material. The base of the xe2x80x9cTxe2x80x9d also provides a frictional component that impedes subsequent plucking of the sheet. Notably, the base of the xe2x80x9cTxe2x80x9d contains a ridge 173 on the trailing side next to the back guide 160 that, due to the weight of the stack on the lowest sheet, can emboss (e.g. indent) the sheets in the stack. The recent use of non-stick coating has not effectively alleviated the friction problem. It has been recognized that the friction is chiefly caused by the embossing on the T-plate ridge. The resulting embossed edge can make it very hard to pluck the sheet from under the weight of the sheets in the hopper. This embossing produces frictional sliding forces far greater than would be predicted by hopper weight and coefficient of friction calculations.
Excessive plucker sliding forces can scratch or scuff the sheets. Excessive sliding forces can also cause a sheet misfeed as the plucker tears the sheet""s edge off, rather than drawing the sheet fully from the stack.
The sucker peels the sheet down towards two metal lips or shelves 250 (FIG. 6). When the sucker peels the sheet down, a finger 212 withdraws and returns to hold the edge of the sheet in the singulated state against the shelves. The shelves are provided for registering the sheets, and their angle is adjustable by plastically deforming (bending) the metal. This angular bending compensates for several other misadjustments, and the shelves, hence, assist in singulating the sheets as the sucker pulls each of the sheets between the shelves.
There is a particular disadvantage to the prior art shelves. Since the edges of the shelves are parallel, sheets of a certain stiffness can become lodged or wedged within the shelves"" parallel gapexe2x80x94effectively bowed and pinched between the two inner edges of the shelves. This is particularly troublesome because the gripping throat of the plucker""s jaws is limited, and therefore the position in which the sheets are held becomes critical. The throat of the jaws is less than one-quarter inch when opened, and it will not pluck successfully unless the material is held within that tolerance.
Finally, it has been recognized that, when the plucker attempts to pull the singulated sheets from the hopper, it has many forces to overcome. First, it must overpower the sliding friction forces produced by the coefficient of friction of the bottom sheet against the floor plate. Then the gripper must tug against forces caused by (a) fiber-lock between uncoated paper sheets, (b) static electricity forces that bind the sheets together, (c) adhesion due to surface tension, and (d) ink or adhesive between adjacent sheets that has oozed and/or dried. Sheets may also contain secondary sheets such as refrigerator magnets, medallions or small parts that must be slid from under the weight of a hopper full of these sheets. There is no present method for reducing or overcoming these various resistance forces between the bottom sheet and the adjacent sheet(s) in the stack.
There have been various prior attempts to address inserter feed hopper and feed mechanism unreliability problem. There are several Bell and Howell patents suggesting solutions, such as U.S. Pat. Nos. 3,844,551, 3,965,644, 4,411,416, 4,013,283. However, at this date, Bell and Howell and their competitors still offer a hopper design that has remained essentially unchanged for decades.
This invention overcomes various disadvantages of the prior art by providing an improved hopper and singulating/feed assembly for a utilization device, such as an inserter, that feeds sheet-like materials from a hopper feed stack that reduces the various geometrical and physical problems that lead to jams, misfeeds and failures to properly singulate the stack. Notably, a hopper that reduces the pressure on the bottom sheets of the stack by providing a parallel wedge structure at the stack base is provided. This wedge structure also helps to drive bottom sheets successively forward toward a front face so as to further break frictional and adhesive contact between sheets at the bottom of the stack. Hopper side guides are provided with integral angled shelves that engage front side edges of the stack and allow easier singulation of respective bottom sheets. Likewise a fixed sucker block assembly is provided, which seats a suction cup in a rotating base with a surrounding planar block face and an integral fulcrum edge for improving the separation of the bottom sheet from the overlying stack. The block face is adjusted to lift the stack upon engagement for further aid in singulation. This block is also fixed in rotation and vertical position with respect to the stack, requiring no continual adjustment. There are also lower shelves upon which the sheet is driven as the sucker rotates away from the stack that have non-parallel sides to avoid binding, and more accurately locate the sheets for subsequent draw into a raceway by a gripper/plucker assembly. A central roller is provided between the front face of the hopper bottom and the rear guide so as to reduce friction during draw of a sheet forwardly. The parallel wedge, structure, likewise, can include a rear angled edge with short (forward-extension) base for supporting the rear of the bottom sheet of the stack that reduces friction. Overall, the of support area for the bottom of the stack (front shelves, rear shelf and roller) is minimized while still maintaining sheets in a positively supported orientation until drawn by the sucker.
According to further embodiments, the sucker block can includes a valve for varying the vacuum flow passing through the suction cup. The block can include a front edge that supplies a variable airflow to the stack to balance the suction force and assist in breaking up the sheets for better singulation. The block can be centered or offset with respect to the stack. Alternatively, a plurality of side-by-side blocks can be used on the stack. The blocks can be arranged to engage the stack at time-separated intervals by for example, varying their length and/or rotational positioning on a common rotating shaft. The shaft can be driven at a variable rotational rate so that respective bottom sheets are initially drawn from the stack at a slower rate by the sucker than the subsequent rate of rotation/draw into a final position to be pulled away by a plucker assembly (at a point resting on the non-parallel shelves). The hopper can be provided with anti-static bars to reduce attraction between sheets. Likewise, a variety of air sources/air knives can be used to selectively direct break-up air at the stack at various times. The hopper""s angled rear edge can be the lower part of an adjustable rear guide that is sized shorter than the length of the sheets to induce a small trough-shape (via gravitational droop) to further stiffen the respective bottom sheets as they are drawn from the stack.